Seldom has any new diagnostic approach been embraced with such initial enthusiasm followed by as much disappointment as the exhaled breath condensate (EBC) approach. It was hoped that this procedure could be used to detect abnormalities in the concentrations of inflammatory and other mediators in the fluid that lines the epithelial surfaces of the lungs (often referred to as the epithelial lining fluid [ELF] or the airway lining fluid). Nearly 500 publications about the EBC approach have appeared in the medical literature since 1996. The appeal of EBCs is readily understandable, because they can be collected by simply cooling the exhaled air. Analysis of the EBC could, in theory, supplant much more inconvenient, expensive, and even dangerous interventions, such as BAL or induced sputum production. However, success with EBC has been thwarted by the extreme and variable dilution of ELF droplets by water vapor, which varies between 5,000 × and 25,000 ×.1-5 This water vapor is generated as a gas in the lungs and only becomes a liquid with cooling. Out of every milliliter of condensate, only ∼ 0.1 μL is released as droplets in the respiratory tract, yet transport of all nonvolatile solutes (eg, urea, electrolytes, and cytokines) from the lungs to the environment is mediated by this relatively small volume of respiratory droplets.